Modern communications networks may be composed of a variety of different networking technologies, and therefore, modern mobile handsets are often capable of operating in more than one type of network. For example, a subscriber may roam between a 2G network and a session initiation protocol (SIP)-based network while using a mobile dual mode handset device. Exemplary 2G networks include global system for mobile communications (GSM), code division multiple access (CDMA) networks, and time division multiple access (TDMA) networks. Similarly, exemplary SIP-based networks include WiFi, worldwide interoperability for microwave access (WiMAX), Internet multimedia subsystem (IMS), and next generation network (NGN) networks. Because these different networks may use various signaling messages and network nodes to establish calls between subscribers, the steps for determining the availability and location of a destination subscriber may differ depending on the type of network to which the subscriber is connected.
For example, when a mobile subscriber initially connects to a 2G network, the subscriber's mobile handset registers with a home location register (HLR) storing location information for the subscriber's handset. The stored location information may include network identification information associated with a mobile switching center (MSC) currently serving the subscriber, such as a network node number (NNN) identifier. Therefore, when the subscriber receives a call originating from another 2G network subscriber, the originating MSC for that call attempts to locate the MSC currently serving the destination subscriber's handset. This determination may include querying the HLR associated with the destination subscriber in order to determine whether the destination mobile subscriber device is available to receive the call as well as its current location.
However, problems arise when the destination subscriber is roaming in a SIP-based network because a conventional HLR located in a 2G network does not contain routing information for SIP-based network nodes. Therefore, one conventional solution for providing interoperability/roaming of mobile subscribers between 2G and SIP-based networks is to store additional information in the HLR indicating the SIP-based network node serving a roaming destination subscriber.
One problem associated with this conventional method for processing calls traversing between 2G and SIP-based networks is that the HLRs may be overly burdened by having to respond to the large number of routing information request queries requesting mobility location information for delivering such calls. Specifically, as the number of subscribers and routing information request queries associated with these calls increases, so too does the amount of processing resources that must be used to process them. Moreover, modification of the widely deployed system of HLRs in existing 2G networks may be cumbersome and expensive. Therefore, it is desirable to networks operators to have a mobility management solution which includes an inexpensive and feasible modification to existing HLRs and operates transparently to mobile subscribers.
Accordingly, a need exists for improved methods and systems for routing a call from a 2G network to a SIP-based network.